It has long been recognized that it is desirable to capture failed blades in a turbofan engine so that failed blade fragments will not damage an operating engine. This need is particularly emphasized in the case of an airborne aircraft which experiences blade failure during the course of a flight. That the aircraft engines remain operating, is of course, a paramount concern. The prior art illustrates various apparatus for blade containment. In general, however, such apparatus includes an annular shroud member having a wall adjacent a blade airfoil, this wall is designed to accommodate and retain a detached blade or blade portion. The wall may be formed with honeycomb material or other energy absorbent, deformable materials capable of capturing blade fragments. Other apparatus may include a containment space overlaid by a penetrable material so that fragments may be captured in the containment space. In general, an area has typically been provided outside the fan flowpath incorporating some form of containment material so that a failed or released fan blade is nested out of the way of trailing blades in the fan.
FIG. 1 illustrates a conventional containment system positioned above fan blade 2, with the forward airfoil release trajectory being represented by line 6 and the aft airfoil release trajectory being represented by line 8. Blade 2 is contained by the containment housing 10 which is made of Kevlar or other appropriate containment material. The interior of the containment housing 10 represents a nesting area 12 which serves to collect the detached blade parts and keeps the blade parts from damaging the unreleased blades. Blade tip 14 and blade root 16 are shown in the nesting area 12 for purposes of illustration.
The type of containment system depicted in FIG. 1 has worked well for shrouded fan rotors with fan blades having relative high aspect ratios (e.g., 3.9 to 4.4). However, for recently developed fan blade systems with blade aspect ratios of 2.1 to 3.0 (wide chord), the nesting area will become very large and add much weight to the containment system.
Therefore, a need exists for a containment system which is able to effectively absorb failed and fragmented composite or hollow titanium, low aspect ratio fan blades while minimizing containment system weight.